The NY Times cites a report by IHS CERA, an energy consulting firm, that Canadian oil sands produce more CO2 through their life cycle than oil derived from regular sources. The report recommends research into how to cut the amount of natural gas used in production, which should improve the picture somewhat.
Canada's oil sands have far less political risk to mine than oil in the Middle East and Africa. They should be under consideration as to energy security. However, that should be balanced against the need to cut CO2 emissions as far as possible.